Geophysics: History on the Rocks

The reporters were accustomed to more stimulating press-conference re freshment. But if the Coca-Cola served at the Pentagon last week seemed bland, the ice that cooled it was something else again. That ice, announced Army scientists, was formed from snow that fell around the time that Christ was born. It had been taken from 1,800 ft.

below the surface of the Greenland ice sheet by an Army team that had drilled to a record depth of 4,550 ft.

To retrieve ancient ice, Army engi neers, led by Physicist B. Lyle Hansen, used a thermal drill with a hollow, elec trically heated head that melted its way down through the sheet, while leaving a 51-in. ice core intact inside it. Every 5 ft. the drill was stopped so that the core could be returned to the surface for study.

At the Army’s Cold Regions Re search and Engineering Laboratory at Hanover, N.H., Geologist Chester Lang-way Jr. has been dating the ice cores both by counting the yearly layers —much as the age of a tree is determined by counting its rings — and by isotope dating of bubbles of ancient air trapped when the ice was formed. Samples tak en from the bottom of the sheet have been found to be as much as 10,000 years old. The ice and the trapped air bubbles are also being analyzed for composition, organic and inorganic im purities, influences of climate and other characteristics that add up to a polar history of the earth over the past 100 centuries.

Though thorough analysis is far from finished, Army scientists have already made a number of notable findings.

For reasons that they do not under stand, the amount of cosmic dust that falls on the earth — now about 2,000 tons daily — has trebled in the past 750 years. They have discovered that ice and snow accumulations during the Viking age (9th and 10th centuries) vary little from the present and that 1776 was an unusually warm year.

They also found that the temperature at the bottom of the ice sheet was a cozy 9°F. — much warmer than the — 13°F. surface temperature because of heat flow from the earth’s interior.

While study of the Greenland ice sample continues, the Army drilling team has already packed up and head ed for Antarctica, where it plans to bore through the southern ice sheet to reach layers estimated to be as much as 90,000 years old.